1. Field of the Invention
The present invention relates to an upper tool holder apparatus for a press brake, and a method of holding the upper tool by the upper tool holder apparatus for a press brake. More specifically, the present invention relates to an upper tool holder apparatus which can adjust the upper tool position and exchange an upper tool with another one easily. Further, the present invention relates to an upper tool holder apparatus and a method of holding the upper tool by the upper tool holder apparatus under a constant upper tool clamping force whenever the upper tools are exchanged.
2. Description of Related Art
A press brake is provided with an upper table (referred to as an upper apron, sometimes) and a lower table (referred to as a lower apron, sometimes) in mutually opposing positional relationship with respect to each other. Further, any one of the upper and lower tables is driven in the vertical direction as a ram.
Further, in the press brake, an upper tool (referred to as a punch) is attached to the upper table and further a lower tool (referred to as a die) is attached to the lower table in order to bend plate-shaped work to various desired shapes.
In the above-mentioned construction of the press brake, when the movable-side table is moved up and down to engage the upper tool with the die, the work positioned between the upper tool and the die can be bent.
In the press brake, in general, since the upper tools must be exchanged according to the bending shapes of work, a number of upper tool holders are arranged on the lower portion of the upper table. That is, a plurality of upper tools are supported by a plurality of upper tool holders so as to be exchanged with respect to each other.
In the conventional upper tool holder apparatus, an upper tool clamp member is attached to a holder body mounted on the lower portion of the upper table, and further fastened by use of fastening bolts, so that the upper portion of the upper tool can be strongly clamped between the holder body and the upper tool clamp member.
In the conventional upper tool holder, therefore, in order to exchange a plurality of upper tools attached to the upper table, a plurality of fastening bolts of the upper tool holder members must be rotated, thus causing a problem in that the upper tool exchange work is troublesome.
To overcome this problem, an upper tool holder apparatus such that the upper tools can be fastened or unfastened by use of an air cylinder mounted on the upper tool holder apparatus has been developed.
In the upper tool holer apparatus of this type, however, since an air cylinders must be provided for a plurality of upper tool holder apparatus, respectively and since an air source is additionally necessary, there exists another problem in that the construction of the upper tool holder apparatus is complicated and thereby the cost thereof is relatively high.
Further, in the conventional upper tool holder apparatus, there exists such a danger that the upper tool drops when the upper tool is released from of an upper tool clamping force of the upper tool holder apparatus.
Further, in the conventional upper tool holder apparatus, the upper tool clamp member must be half fastened to such an extent that the upper tool does not drop for alignment with the die, and after that the upper tool clamp member must be full fastened tightly after the upper tool and die have been aligned with each other. As a result, there exists another problem in that the tool setting work is troublesome.
As prior art examples related to the present invention, there are EP 0 387 121 A1 (the first prior art) and Japanese Published Unexamined (Kokai) Patent Application No. 6-23436 (the second prior art).
In the first prior art press brake, although the upper tool can be clamped between the upper clamp member pivotally supported by the upper table and the holder body, since the upper tool must be attached to or removed from the upper table by pivoting the upper tool so as not to interfere with a pivotal axle of the upper tool clamp member; that is, since the upper tool must be pivoted by supporting the upper tool as heavy as 20 to 30 kg manually on the front side of the press brake, there exists a problem in that this work is dangerous for the worker (in particular for the worker's hand and waist.
In addition, when a plurality of upper tools are clamped by connecting the upper tools in the longitudinal (horizontal) direction thereof, there exists a problem in that it is impossible to insert and connect an end of another upper tool between and with the already clamped upper tools so that a plurality of upper tools can be arranged in a longitudinal direction thereof.
Further, in the first prior art press brake, since the upper tool is clamped between the upper tool clamp member (pivotally supported by the upper table) and the holder body, the upper tool must be exchanged by pivoting the upper tool so as not to interfere with a pivotal axle of the upper tool clamp member, so that there exists another problem in that the shape of the upper tool is not simple, that is, complicated and thereby the upper tool cannot be processed easily.
In the second prior art press brake, the upper tool can be attached to or removed from the upper tool holder apparatus by pivoting an operation lever provided on the upper tool holder apparatus from a clamp position to an unclamp position or vice versa to facilitate the upper tool exchange. However, the upper tool is exchanged by the upper tool holder apparatus by shifting the upper tool in the longitudinal (the right and left) direction, when some upper tool elements of a series of the split type upper tools of different lengths are required to be exchanged at the middle portion thereof, there exists a problem in that the upper tool exchange work is rather troublesome.
Here, the conventional upper tool holder apparatus (not the prior art) will be explained in further detail with reference to FIGS. 25A and 25B. In the drawings, an upper tool clamp member 403 is attached to an upper holder body 401 fixed to a lower portion of an upper table (not shown). Therefore, an upper tool 407 can be fixed or clamped between the clamp member 403 and the upper tool holder body 401 when the clamp member 403 is fastened by use of a fastening bolt 405. Therefore, whenever the upper tools 407 are required to be exchanged with other upper tools, a great number of fastening bolts 405 must be rotated to unfasten and fasten the upper tool clamp members 403, with the result that the upper tool exchange work is troublesome.
Further, in the upper tool 407, it is desirable that an angle ulower end surface 409E of an upper support portion 409 of the upper holder body 401) and a sliding surface 407F slidable in contact with a vertical surface 409F of the upper tool support portion 409 is formed accurately at 90 degrees in correspondence to the angle between the lower surface 409E and the vertical surface 409F of the upper support body 409. In general, however, this angle is process as .theta.&lt;90 degrees to prevent .theta.&gt;90 degrees under consideration of the processing error. The reason is as follows: if .theta.&gt;90 degrees, as shown in FIG. 25A exaggeratively, a gap is produced between the lower end surface 409E of the upper tool support portion 409 and the shoulder portion 407S. Therefore, when work is bent, the upper tool 407 is deformed in a direction that this gap is reduced. As a result, the lower end portion 407E of the upper tool 407 is deformed relatively large (due to the punching pressure) in accompany with this deformation due to the pressure of this gap, thus degrading the bending precision.
On the other hand, if .THETA.&lt;90 degrees, as shown in FIG. 25B exaggeratively, a gap is produced between the vertical surface 409F of the upper tool support portion 409 and the sliding surface 407F of the upper tool 407. Therefore, when the upper tool clamp member 403 is fastened strongly by the fastening bolt 405, since the upper tool 407 is deformed in such a way that the gap is reduced, there exists the case where the lower end portion 407 E of the upper tool 407 is dislocated slightly.
Here, since the fastening force applied to the fastening bolt 405 differs according to the worker, the deformation at the lower end portion 407E of the upper tool 407 differs according to the worker and/or worker's fatigued conditions.
Therefore, in the work bending processing by exchanging the upper tools, even if the above-mentioned angle is formed so precise as to lie within an allowable range, there exists a problem in that a high precise bending processing cannot be achieved, when the upper tools cannot be exchanged at a high upper tool exchange reproducibility.